Production of glycine betaine and dimethylsulfoniopropionate in marine phytoplankton. I. Batch cultures

The quantitative significance of the nitrogenous compound glycine betaine ( GBT) and its sulfur analog dimelhylsulfoniopropionate (DMSP) to intracellul ar pools in marine phytoplankton is not well known. In a series of experime nts conducted in August 1993, we measured these compounds, as well as total organic sulfur, carbon, and nitrogen, over the growth cycle in six isolate s of marine phytoplankton, Amphidinium car ferae Hulburt, Chrysocromulina s p. Lackey, Emiliania huxleyi Hay et Mohler, Prorocentrum minimum (Pavillard ) Schiller, Skeletonema costatum (Greville) Cleve, and Tetraselmis sp. At t he same time, we measured cellular concentrations of protein, amino acids, chlorophyll, and inorganic nutrients. All six species produced DMSP, while three produced GET at lesser levels. In the Chrysochromulina sp. isolate, l evels of GET were greater than DMSP during the exponential phase of growth, but declined sharply as the culture approached stationary phase. This chan ge appeared to coincide with the onset of nitrogen limitation. Other nitrog enous osmolytes were produced in five of the six species but in much smalle r quantities. DMSP contributed significantly to cellular sulfur throughout the growth cycle although, in some algae, the proportion of dissolved DMSP increased substantially during stationary growth. When present, GET formed a sizeable fraction of the cellular nitrogen only during exponential growth . A significant percentage (ca. 50%) of the organic nitrogen could not be a ccounted for even when cellular pools of protein, amino acids, inorganic ni trogen, and nitrogenous osmolytes were combined. Based on these experiments , there does not appear to be a reciprocal relationship between DMSP and GE T production, although GET production does appear to be correlated with nit rogen availability.